Voltage control system



g- 1959 J.F. O'DONNELL ET AL 2,398,514

VOLTAGE CONTROL SYSTEM Filed March 13, 1956 TIME DEL Y DEVICE -4 1 [1 CRa) i 21 1 P 13 -0 1 VOLTAGE LOAD I REGULATOR O F'IG: l

RL I, RLO RLh RATED 1 OUTPUT VOLTAGE RL'i.

U f5 F IG. 2 a I 33 RLc S 31 O EIQ I LOAD CURRENT-PERCENT OF RATED FULLLOAD RATED LOAD CURRENT F'IG'. 3 11,1 0 VOLTAGE To 7 T1 INVENTOR.

' JOHN F. O'DONNELL BY DONALD SEGALL AGE NT United States atent2,893,514 Patented Aug. 4, 1959 ice VOLTAGE coNrnor SYSTEM John F.ODonnell, Apaiachin, and Donald Segall, Vesta], N.Y., assignors toInternational Business Machines gorporation, New York, N.Y., acorporation of New ork Application March 13, 1956, Serial No. 571,183 8Claims. (Cl. 315106) This invention relates to voltage control systems,and particularly to a voltage control system adapted to supply power toa load having an impedance which varies from a relatively low initialvalue to some higher value as a result of energization. Moreparticularly, the present invention is directed to an improved voltagecontrol system for governing the supply of power to the filaments, orcathode heaters, of electron discharge devices.

The energization of a relatively large number of electron dischargedevices, such as the vacuum tubes employed as functional units in anelectronic computer, for example, presents a diflicult problem from thevoltage control standpoint. When the load is first energized, theso-called cold resistance thereof is relatively low, representing, forexample, only one-seventh of the so-called hot resistance which existsafter the filaments are heated to their normal operating temperature atrated voltage and current. Moreover, when such a load is in its normaloperating condition, the voltage must be carefully controlled since itis Well known that over-voltages are deleterious to vacuum tubefilaments or heaters, and undervoltages will not, of course, supplysulficient power for proper emission.

It has heretofore been proposed to provide suitable means for limitingthe inrush current to tube heaters by the use of suitable limitingimpedances, or by the use of a multi-tap transformer, with suitableswitching means for switching the limiting impedance out of the supplycircuit, or for changing the transformer taps as the tubes warm up. Sucharrangements are open to the general objection that the transitionrequires more than two steps if it is to take place relatively smoothlyand without exceeding the maximum permissible input current, so that theswitching apparatus is relatively complex.

Continuously variable transformers or limiting impedances have also beenemployed in this capacity, but these devices are relatively expensive,and the motor drives used to operate them automatically are relativelycomplex and costly.

Considering the problem of maintaining a substantially constantoperating voltage for vacuum tube heaters or filaments, numerous typesof voltage regulators, well known in the art, have been employed forthis purpose.

It is an object of the present invention to provide an improved voltagecontrol system for a load which pro vides inrush current limitation to aload which increases in impedance after energization, and whichmaintains a substantially constant voltage across the load after theload reaches its normal operating impedance value.

Another object of the invention is to provide a voltage control systememploying a voltage regulator having a drooping voltage-versus-currcntoperating characteristic to limit the inrush current to a load having alow initial impedance which changes to some higher operating impedance,at which value the voltage supplied thereto is maintained substantiallyconstant.

A further object of the invention is to provide a voltage control systemfor governing the supply of energy to the heaters or filaments ofelectron discharge devices in which a voltage regulator having adrooping voltageversus-current characteristic is employed both as an inrush current limiter and a. voltage regulator.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of examples, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. 1 is a schematic circuit diagram of a voltage control system inaccordance with a preferred embodiment of the invention.

Figs. 2 and 3 are graphs illustrating the operation of the arrangementshown in Fig. 1.

Referring now to Fig. 1, there is shown in simplified form anarrangement for controlling the voltage supplied to a load 1 from asuitable source of energy such as the alternator 3. Power is suppliedfrom the alternator 3 to the primary winding 5 of a transformer 7 whenthe contacts 8 and 9 of a control switch are closed. A first secondarywinding 11 or a second secondary winding 13 are connected to inputterminals 15 and 17 of a voltage regu lator 19 in accordance with theposition of contacts 21 and 23 of a control relay CR. The outputterminals 25' and 27 of re ulator 19 are connected to the load 1. RelayCR is energized by power supplied from the alternator when the switch SWis closed, after the expiration of a suitable time interval determinedby a time delay device 29.

Before explaining the operation of the arrangement shown in Fig. 1, itis necessary to consider the voltageversus-current characteristics ofthe voltage regulator 19, and the impedance characteristics of the load1, which are depicted graphically in Fig. 2.

Considering first the voltage regulator 19, the actual form orconstruction of the regulator is immaterial to the present invention,the only necessary requirement being that the voltage-versus-currentcharacteristic of the regulator must be of the general form illustratedby the curves Biz: and E111 of Fig. 2. Curve Ela. shows that withnominal or rated input voltage the output voltage of the regulatorremains substantially constant for all values of output current up to100 percent of rated full load, after which the voltage drops off rathersharply so that for relatively large overload currents, the outputvoltage drops to zero. Curve Elb illustrates the relation of the outputvoltage and current for an input voltage substantially less than ratedor nominal input voltage, for example, 50 percent of rated inputvoltage, wherein the output voltage remains substantially constant forcurrents up to 40 or 50 percent of full load current, and then drops offsharply so that the output voltage is reduced to Zero for load currentsof the order of percent of full load value. The values given are onlyapproximate and illustrative, and other limits may be as readily established, the only important feature being the relatively sharp drop inthe curve after full load current is exceeded.

It will be obvious to those skilled in the art that many types ofvoltage regulators may be designed to have such characteristics ofoutput voltage-versus-current, and accordingly it is deemed unnecessaryto show any specific structure for the voltage regulator 19.

Considering now the impedance characteristics of the load 1, the dashedline RL of Fig. 2 illustrates the chang ing impedance characteristics ofthe load. Since a preferred use of the invention is to control the powersuppliedto vacuurntube heaters, the curve RL illustrates the manner inwhich the voltage and current vary 111 a load such as one or more vacuumtube heaters, as a result of the change of resistance with heating.Since the res1stance change with respect to temperature is non-linear,the characteristic curve RL is curved as shown. A series of straightlines designated by the reference characters RLc, RLi, RL]! and RLo areprojected values of the characteristic curve RL taken at differentpoints, and represent the load impedance for different conditions oftime, in this particular instance. For example, the line RLc representsthe impedance of the load 1 at the time of initial energization, anypoint along the line representing the ratio of E divided by 1. Likewisethe impedance at successively later intervals of time followingenergization is represented by the lines RLi, RL/z and RLo, in the ordergiven. It will be seen therefore that the load to be supplied by thesystem according to this invention is one which changes its impedancefrom a relatively low initial value when first energized to some highervalue or series of values following energization, and which maintains arelatively stable impedance value at any predetermined level ofenergization after having reached that value. Thus the arrangement isespecially adapted for controlling the energy to vacuum tube heaters,which exhibit this type of impedance characteristic, but is not limitedto this application.

Having thus considered the characteristics of the regulator 19 and theload 1, the operation of the invention as illustrated in Fig. 1 will nowbe described.

When the switch is closed, its contacts 8 and 9 complete the circuit forsupplying power from the source 3 to the primary winding of transformer7. Relay CR is released at this time, and will remain released until theexpiration of a predetermined time delay introduced by time delay device29. The details of the time delay device are not shown since it may takeany one of a number of forms well known in the art, and its detailedconstruction forms no part of the present invention. Suffice to say thatthe control relay CR is energized only after a predetermined timeinterval has elapsed following the closing of switch SW.

Energy issupplied at this time from the secondary winding 11 oftransformer 7 over the unoperated contacts 21 and 23 of relay CR toinput terminals 15 and 17 of voltage regulator 10. The parts areconstructed and arranged so that the voltage at terminals 15 and 17 atthis time is some value substantially less than the nominal or ratedinput voltage, so that the voltage regulator output voltage at terminals25 and 2.7 is expressed by curve Elb of Fig. 2.

With the load 1 at its initial or low impedance value, as shown by theline RLc of Fig. 2, the initial operating voltage and currentestablished at the closing of switch SW is determined by theintersection of the plots. It can be seen that the voltage is relativelylow and that the current is limited to a value of the order ofapproximately 80 percent of rated full load.

In the particular case where the load 1 is the heater or filamentcircuit of one or more vacuum tubes, the value RLc would represent theimpedance of the load with the heaters cold. In similar fashion, thevalues RLi, RLIz and RLo would represent points selected along the curveRL as the impedance increases from its initial cold value, through anintermediate value, a hot value and finally to an operating value atrated voltage and current.

As the impedance of the load increases following initial energization,the voltage will rise along curve Elb, from point 31, through point 33,to some point 35, in some predetermined time interval determined by thenature of the load. For example, in the case of vacuum tube heaters, thetime required for the impedance to change from RLc to RLh may be of theorder of 25 seconds.

It can be seen from curve Elb that during the rise in voltage from point31 to point 35, the current to the load will remain substantiallyconstant and less than the full load value.

After the expiration of the predetermined time interval, correspondingto the delay time of time delay device 29, the relay CR is energized andits contacts transfer the input connection of voltage regulator 19 fromsecondary winding 11 to secondary winding 13 of transformer 7. The partsare proportioned and arranged so that the supply of energy to regulator19 from secondary winding will cause the output of regulator 19 tofollow the curve Ela of Fig. 2.

With the resistance of the load at this time represented by the lineRL/z of the graph, it will be seen that the voltage and current willimmediately jump to the intersection of curve EM and line RLh,designated by the reference character 37 At this point, the current isslightly over the rated full load current, but is not excessive. Theoutput voltage will be increased from its previous value to some valueslightly lower than rated output voltage.

The voltage will new build up slowly to rated output voltage, and thecurrent will decrease to its rated full load value, defined by theintersection of curve Ela and line RLo, point 39, which can be said tobe the normal operating point of the system.

Following the arrival of the system at its stable operating point, thevoltage regulator then operates in its normal manner to maintain theoutput voltage constant despite fluctuations in the voltage supplied tothe input of the regulator.

Upon shut down all parts are restored to their original condition, asinitially described, and subsequent restarting will follow the operationdescribed above.

The operation of the system in providing a slow build up of load voltagewithout excessive overload current is depicted graphically in Fig. 3, inwhich the variations of load current and voltage are plotted againsttime. When the control switch is closed, at time T the voltage andcurrent immediately assume certain values, each substan tially less thanrated. The voltage then increases gradually until the expiration of thetime delay interval at time T while the current remains substantiallyconstant at some value less than its full load value. At time T thevoltage jumps to some increased value, still less than rated value andthe current jumps to some value greater than full load value. Thevoltage then builds up slowly to its rated value, and the currentdecreases to its full load value, after which the voltage and currentare maintained substantially constant.

A number of variations in the arrangement of the system are possible.For example, the control of the voltage supplied to the input ofregulator 19 may involve more than two steps, as herein shown anddescribed. Various arrangements for supplying the different inputvoltages are possible, such as, for example, the use of anautotransformer for transformer 7 rather than a transformer havingseparate secondary windings.

From the foregoing, it will be seen that a voltage control systemaccording to the invention advantageously employs the droopingvoltage-versus-current characteristic of a conventional voltageregulator to govern the supply of power to a load having an impedancewhich changes following energization. The arrangement is economical anduncomplicated and does not interfere with the normal function of theregulator.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in theart, without departing from the spirit of the invention. It is theintention, therefore, to be limited only as indicated by the scope ofthe following claims.

What is claimed is:

l. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising voltage regulating means having inputand output terminals and characterized by an output voltage-versusoutputcurrent relation in which, for a predetermined normal value of regulatorinput voltage, the regulator output voltage remains substantiallyconstant for values of output current between zero and full load valuesand then decreases sharply to zero voltage for values of output currentsubstantially in excess of full load, means for connecting said load tosaid voltage regulator output terminals, a first source of energy havinga nominal voltage equal to said predetermined normal value of regulatorinput voltage, at least one other source of energy having a nominalvoltage substantially less than said predetermined normal value of saidregulator input voltage, and means for sequentially connecting saidsources of energy to the input terminals of said voltage regulator.

2. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising voltage regulating means having inputand output terminals and characterized by an output voltageversusoutput-current relation in which for a predetermined normal valueof regulator input voltage, the regulator output voltage remainssubstantially constant for values of output current between zero andfull load values, and then decreases sharply to zero voltage for valuesof current substantially in excess of full load, means for connectingsaid load to said voltage regulator output terminals, a first source ofenergy having a nominal voltage equal to said predetermined normal valueof regulator input voltage, a second source of energy having a nominalvoltage substantially less than said predetermined normal value ofregulator input voltage, and means for sequentially connecting saidsources of energy to the input terminals of said voltage regulator.

3. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising voltage regulating means having inputand output terminals and characterized by an output voltageversus-outputcurrent relation in which, for a predetermined normal value of regulatorinput voltage, the regulator output voltage remains substantiallyconstant for values of output current between zero and full load values,and then decreases sharply to zero voltage for values of currentsubstantially in excess of full load, means for connecting said load tosaid voltage regulator output terminals, a first source of energy havinga nominal voltage equal to said predetermined normal value of regulatorinput voltage, a second source of energy having a nominal voltagesubstantially less than said predetermined normal value of regulatorinput voltage, means for initially connecting said second source ofenergy to said input terminals of said voltage regulator for initialenergization of said load, and means for subsequently disconnecting saidsecond source of energy and connecting said first source of energy tosaid input terminals of said voltage regulator for normal and continuedenergization of said load.

4. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising voltage regulating means having inputand output terminals and characterized by an output voltageversus-output current relation in which, for a predetermined normalvalue of regulator input voltage, the regu lator output voltage remainssubstantially constant for values of output current between zero andfull load values, and then decreases sharply to zero voltage for valuesof current substantially in excess of full load, means for connectingsaid load to said voltage regulator output terminals, a first source ofenergy having a nomi nal voltage equal to said predetermined normalvalue of regulator input voltage, a second source of energy hav-' ing anominal voltage substantially less than said predetermined normal valueof regulator input voltage, means for initially connecting said secondsource of energy to said input terminals of said voltage regulator forinitial energization of said load, and means effective after the elapseof a predetermined time interval following the initial energization ofsaid load for disconnecting said second source of energy and connectingsaid first source of energy to said input terminals of said voltageregulator for normal and continued energization of said load.

5. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising voltage regulating means having inputand output terminals and characterized by an output voltageversus-output current relation in which, for a predetermined normalvalue of regulator input voltage, the regulator output voltage remainssubstantially constant for values of output current between zero andfull load values, and then decreases sharply to zero voltage for valuesof current substantially in excess of full load, means for connectingsaid load to said voltage regulator output terminals, a first source ofenergy having a nominal voltage equal to said predetermined normal valueof regulator input voltage, a second source of energy having a nominalvoltage substantially one-half of the value of said predetermined normalvalue of regulator input voltage, means for initially connecting saidsecond source of energy to said input terminals of said voltageregulator for initial energization of said load, and means operativeafter a predetermined time interval following the initial energizationof said load for disconnecting said second source and connecting saidfirst source to the input terminals of said voltage regulator for normaland continued energization of said load.

6. A voltage control system for governing the power supplied to a loadcomprising the emission-producing elements of at least one electrondischarge device, comprising, in combination, voltage regulating meanshaving input and output terminals and characterized by an outputvoltage-versus-output current relation in which, for a predeterminednormal value of input voltage, the output voltage remains constant atthe rated normal voltage for said load for values of output current fromzero to full load value, and thereafter decreases sharply to zerovoltage for current values substantially greater than the rated fullload current for said load, means for connecting said load to saidvoltage regulator output terminals, a first source of energy having anominal voltage equal to said predetermined normal value of inputvoltage, a second source of energy having a nominal voltage equal tosubstantially onehalf the value of said predetermined normal value ofinput voltage, a control relay, means including contacts of said controlrelay for sequentially connecting the input terminals of said voltageregulator to said first and said second source of energy, meansincluding a time delay device for operating said relay at the expirationof a predetermined time interval following the initial energization ofsaid load, control means effective to govern said initial energization.

7. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising voltage regulating means having inputand output terminals and characterized by an output voltageversus-outputcurrent relation in which, for a predeter mined normal value ofregulator input voltage, the regulator output voltage remainssubstantially constant for values of output current between zero andfull load values, and then decreases sharply to zero voltage for valuesof current substantially in excess of full load, means for connectingsaid load to said voltage regulator output terminals, a first source ofenergy having anominal voltage equal to-said predetermined-normal valueof regulator input voltage, a second source of energy having a nominalvoltage substantially one-half of the value of said predetermined normalvalue of regulator input voltage, means for initially connecting saidsecond source of energy to said input terminals of said voltageregulator for initial energization of said load, and means operativeafter a predetermined time interval following the initial energizationof said load for disconnecting said second source and connecting saidfirst source to the input terminals of said voltage regulator for normaland continued energization of said load, said last-named meanscomprising time delay switching means provided with transfer contactswhich transfer the connection of the input of said regulator means fromsaid second source to said first source at the expiration of saidpredetermined time interval.

8. A voltage control system for governing the power supplied to a loadhaving an impedance which increases from a first to a second valuefollowing energization, comprising, in combination, a voltage regulatorhaving input and output terminals and characterized by an output voltageversus output current relation in which for a predetermined normal valueof regulator input voltage, the regulator output voltage remainssubstantially constant for values of output current between zero andfull load values, and then decreases sharply to zero voltage for valuesof current substantially in excess of .full load, means for connectingsaid load to said voltage regulator output. terminals, :1 source. of.energy, transforming means for deriving :fromsaid source energy at afirst voltage value substantiallyzless than saidnormal voltage and at asecond voltage .equal to said normal voltage, control means forconnecting saidsource of energy to said transformingmeans,switching/means effective in a first condition to connect the input ofsaid regulator to said transforming means-toenergizesaid regulator atsaid first voltage value and effective in a second condition to connectthe input of said regulator-to said transforming means to energize saidregulator at said second voltage value, and means governedbyrsaidtcontrol means to initially establish saidswitching means in saidfirst condition and after a predeterminedtime interval to establish saidswitching means in said second condition.

References Cited in the file of this patent UNITE/D sT-AIEs PATENTS1,365,638 Coolidge Ian. 11, 1921 2,048,203 Spencer July 21, 19362,613,289 Warner Oct. 7, 1952 2,654,824 Schroeder Oct. 6, 1953 2,727,975'Molyneaux Dec. 20, 1955 2,769,924 Beery Nov. 6, 1956

